How could the planes wings penetrate the WTC?

WeedWhacker

Senior Member
Which tower is this?
That would be the North Tower, first impact (AAL 11). It was in a shallow left bank.

I would surmise, though, that it was pulling some Gs at the moment of impact. This would cause the additional flexing that I mentioned earlier.
 

jaydeehess

Senior Member.
UA175 was also rolling in a pretty extreme way as it aproached WTC2 and would have had an even greaterupward sweep of its wings.
 

Soulfly

Banned
Banned
I was referring to the angle of the plane in relation to the face of the towers and not the bank of the plane.
 

WeedWhacker

Senior Member
UA175 was also rolling in a pretty extreme way as it aproached WTC2 and would have had an even greaterupward sweep of its wings.
Yes, it was. The hijacker was attempting to correct his aim. Also, he was at a higher airspeed than AAL 11. That combined with a bank angle of (what looks like about 38°) adds more G forces.





(And, of course the image comparison just above came from a CT web page...which continues to draw incorrect inferences and make outrageously faulty claims).
 

Soulfly

Banned
Banned
The one on the left would be more likely to make a plane shaped hole, while the one on the right would be less likely. The angle is exaggerated on the right but even a small angle would make different shaped hole.
plane3.jpg
Picture not to scale.
 

MikeC

Closed Account
I don't think we can say that the steal beams were cut for sure from wing tip to wing top based on the photos.
Others have discussed the dihedral of the wings.

However where or how the beams are cut is quite trivial IMO - the tact remains there are obvious and simple mechanisms by which the wing can enter the building.

that the wing is also stronger than the beams is a reason why the beams may have all be broken/cut/bent to failure - even though aluminium is "softer" than steel - you would not expect thin steel sheet to stop an aeroplane - but a thick steel block would do so - so somewhere in between there are many possible small structures of steel that are not strong enough to resist....just as ther aer many potential large structures that would show more resistance.
 

WeedWhacker

Senior Member
he angle is exaggerated on the right but even a small angle would make different shaped hole.
Oh, what you're getting at is the 'apparent' length of a swept-back wing depending on geometry. (This is an important consideration when taxiing, and in a tight space for wingtip clearance. Especially when there is no marshaller, or "wing Walker" out there for guidance).

But, the net effect (iin terms of the impact opening's shape) would be a fore-shortening of the length of the opening made on the side where the wing impacts last.
 

Soulfly

Banned
Banned
Oh, what you're getting at is the 'apparent' length of a swept-back wing depending on geometry. (This is an important consideration when taxiing, and in a tight space for wingtip clearance. Especially when there is no marshaller, or "wing Walker" out there for guidance).

But, the net effect (iin terms of the impact opening's shape) would be a fore-shortening of the length of the opening made on the side where the wing impacts last.
I'm just thinking, the greater the angle the more surface area of one side of the plane is hitting and would cause the plane to break up different, possibly causing the wing on the far side to not cause as much damage.

Really though at those speeds and the angle doesn't appear to be that great, I'm sure it isn't a big factor.
 

WeedWhacker

Senior Member
I'm just thinking, the greater the angle the more surface area of one side of the plane is hitting and wold cause the plane to break up different, possibly causing the wing on the far side to not cause as much damage.
I believe since we're talking about thousandths of seconds here, it again is probably insignificant.

Found the sort of illustration used in AFMs (Flight Manuals) to show wing sweep effect based on (relative) yaw angles:



Yikes!! That came out poorly.

Here: http://www.boeing.com/assets/pdf/commercial/airports/acaps/767sec4.pdf

(Page 4.2.1)
Untitled.jpg
 
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Jason

Senior Member
It's fascinating (to me) because for pilots it's just intuitive, when we look at the photos of the impact point. Doesn't occur to us that others would have a different conception (or, misconception) of how they 'imagine' the entry damage should appear.
I agree, I'm not a pilot, nor do I rarely ever get a chance to see a plane head on, so its not second nature to me like you and other pilots. Did you have an idea of what the angle of inclination the wing sits at relative to the fuselage.

I believe since we're talking about thousandths of seconds here, it again is probably insignificant.
Found the sort of illustration used in AFMs (Flight Manuals) to show wing sweep effect based on (relative) yaw angles:
I too, don't believe this would have a significant effect on the angle or damage. Why is it that the left side looks to have suffered left damage than the right side though? Is there a reason for that, scientifically speaking?
 

Jason

Senior Member
Which tower is this?
You would also need to take into account the angle of impact. Isn't the 2nd plane that hit kind of turning? Hitting squarely at 90 degrees seems unlikely. That would make one side (wing) of the plane impact a tad bit sooner than the other. Wing could be folded back or just sheered off. Once the plane starts to break up, all bets are off on saying this is what it should look like, as there are so many factors to take into account.
Also based on the photo I pasted, where would the engines' entry be based on that photo
 

Jason

Senior Member
However where or how the beams are cut is quite trivial IMO - the tact remains there are obvious and simple mechanisms by which the wing can enter the building.
What are these "obvious" and "simple" mechanisms you speak of? I believe the blgs were hit by planes, I'm just trying to understand the science behind the destruction they caused, and why there are vast differences between by impacts
 

MikeC

Closed Account
What are these "obvious" and "simple" mechanisms you speak of? I believe the blgs were hit by planes, I'm just trying to understand the science behind the destruction they caused, and why there are vast differences between by impacts
the mechanisms for entering the WTC are obvious and simple - where there were no steel columns the aircraft structure broke the glass.

Where there were steel columns the aircraft structure was deformed to either side, and in doing so also bent and broke the columns.

I'm sorry - but I can't put it any simpler than that.
 

Jason

Senior Member
the mechanisms for entering the WTC are obvious and simple - where there were no steel columns the aircraft structure broke the glass.

Where there were steel columns the aircraft structure was deformed to either side, and in doing so also bent and broke the columns.

I'm sorry - but I can't put it any simpler than that.
I understand that, but can you give me an idea of where the engines would've been in the photo I submitted above please
 

Jason

Senior Member
Also with respect to the pentagon, isn't it true the all of the jet fuel is stored in the planes' wings. If that were the case wouldn't the fire ball have been limited to the exterior of the building since the wings never made it into the building according to the hyposthesis that the concrete structure resisted the wings.
 

Landru

Moderator
Staff member
Also with respect to the pentagon, isn't it true the all of the jet fuel is stored in the planes' wings. If that were the case wouldn't the fire ball have been limited to the exterior of the building since the wings never made it into the building according to the hyposthesis that the concrete structure resisted the wings.
Posting guidelines suggest this is a topic for another thread.
 

Mick West

Administrator
Staff member


I don't think we can say that the steal beams were cut for sure from wing tip to wing top based on the photos.
They were not cut. They were mostly pushed out of the way. The things that failed were the bolts between segments.
 

Jason

Senior Member
Posting guidelines suggest this is a topic for another thread.
Your right Landru, sorry. Saw other threads in here about the pentagon and I was going off of that. I looked up the dihedral affect on wiki and honestly its a bit confusing for the novice but there was a section called this;

What does it mean when they say the dihedral effect is nothing else but the "rolling moment caused by sideslip". Please explain
 

Jazzy

Closed Account
I understand that, but can you give me an idea of where the engines would've been in the photo I submitted above please
The engines are turbofans. The fans are surrounded by immensely strong kevlar composite burst rings and run on massive steel shafts. The compression and exhaust casings are also alloy steel, as are the exhaust turbines.

All steel parts would have had a three times greater energy, weight-for weight, compared with aluminum alloy, and would have become the leading elements of the moving aircraft wreckage moving towards the far side of the tower on each of several floors. The lightest element in the impacting plane was the fuel, but that was still massive enough to help the wings chew through many columns. Where they didn't, they passed through the windows in chunks, deforming and tearing where they had to. The floors were chewed inwards to a depth of up to ten feet by the wing spars before they failed and were chopped up.

Also with respect to the pentagon, isn't it true the all of the jet fuel is stored in the planes' wings. If that were the case wouldn't the fire ball have been limited to the exterior of the building since the wings never made it into the building according to the hyposthesis that the concrete structure resisted the wings.
The plane had a central fuel tank as well as wing tanks, I think. One wing outer section had folded up and immolated itself against the face. But the rest went in, mostly, through a 93 foot wide gap in the ground floor. This has all been covered. It's old ground.

Edit: Only a 757-type aircraft could have created the damage seen at the pentagon. A missile couldn't have chopped lampposts, scooped out a curb segment and put several tons of kerosine into the building. The severe damage to many floor-pillar connections (causing a delayed collapse) could only have been caused by a fuel/air explosion. The only thing likely to have caused greater damage would have been a loaded KC-10 tanker. Or a jumbo jet.
 
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Jazzy

Closed Account
I know that the Forum where this image originated is of a 'CT disposition' but...at least someone made the effort.

But not the effort to remember that the plane was pulling 2G at the time it struck the building. That would have bent the wingtips up ten feet or so.

The wings would have instantly unloaded as they disintegrated, of course, and tried to straighten out.

The fin has only the fuselage tailcone (by this time there's no fuselage left) to react against the downthrust it receives because of its sweep. It would be able to pass within the building without having to cut its way in very much merely by pitching backward.
 
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Jason

Senior Member
But not the effort to remember that the plane was pulling 2G at the time it struck the building. That would have bent the wingtips up ten feet or so.

The wings would have instantly unloaded as they disintegrated, of course, and tried to straighten out.

The fin has only the fuselage tailcone (by this time there's no fuselage left) to react against the downthrust it receives because of its sweep. It would be able to pass within the building without having to cut its way in very much merely by pitching backward.
When you say the plane was "pulling 2G" at the time it struck the bldg, are you inferring this because you think the pilot was pulling up to correct its course before entering into the bldg. Did the plane hit the bldg parallel to the street or did the plane hit the bldg on a downward declination.
 

Jazzy

Closed Account
When you say the plane was "pulling 2G" at the time it struck the bldg, are you inferring this because you think the pilot was pulling up to correct its course before entering into the bldg. Did the plane hit the bldg parallel to the street or did the plane hit the bldg on a downward declination.
No. If you watch all the videos of the airplane's approach, with an understanding of what the airplane has to be doing in order to be in the position it's in, you will understand that the plane was banking as it applied its elevators, and you can see the wings flexing and the elevator movement. They are relatively subtle, but they are there. Head-on shots show this best. Knowing the angle of bank in level flight allows you to calculate the g-force on the airframe directly.

The chances are it was still inclined downward a little - but it was pulling up and to the left. That 2G would have put anyone standing inside the plane on to the floor, unless they could have seen the maneuver coming.
 

WeedWhacker

Senior Member
No. If you watch all the videos of the airplane's approach, with an understanding of what the airplane has to be doing in order to be in the position it's in, you will understand that the plane was banking as it applied its elevators, and you can see the wings flexing and the elevator movement. They are relatively subtle, but they are there. Head-on shots show this best. Knowing the angle of bank in level flight allows you to calculate the g-force on the airframe directly.

The chances are it was still inclined downward a little - but it was pulling up and to the left. That 2G would have put anyone standing inside the plane on to the floor, unless they could have seen the maneuver coming.
Jazzy, I would caution that although your description was apt for UAL 175, the photo that Jason originally posted was of the North Tower damage from AAL 11. Of which there is but one video clip.

In answer to the question by Jason (which is better defined as the airplane's pitch attitude relative to the horizon), I searched a while and found no definitive result. Except for the Purdue animation which is posted in my response #15. (That shows Flight 11 and the North Tower. The video does not specifically name AAL 11, but it does specify the North Tower in its analysis. The video does show a few slight, perhaps 1° to 2° nose-down pitch attitude at impact). Jason again posted an image of the impact entry on the North Tower in post #36, so we are mostly focusing on that.

Confusion between the two events is probably my fault, because in discussing wing dihedral and the effect of flight loads on it, I referred to UAL 175 and the South Tower in post #46.

Those events are very complex, as we all know, and the discussions can stray in order to incorporate all information, which unfortunately sometimes leads to confusion or misunderstandings.
 

jaydeehess

Senior Member.
It refers to the aerodynamics, and the reason for dihedral as it contributes to roll stability.
There seems to be a conflation of terms there. There is a designed, static aircraft dihedral that has the wings slightly upswept. This is evident in the drawings of the aircraft.
The dihedral effect, AFAIK, refers to the dynamic changes in the upsweep of the wing under load( When producing lift for instance)
 

Jazzy

Closed Account
Those events are very complex
But the differences are as relatively subtle as the sines of 0 degrees, 1 degree, or two degrees. That's subtle.

Essentially they both slammed into the towers in horizontal flight, one slightly missing the central axis and not so perpendicular to the tower face. Their roll angles caused more floors to be involved in each case.

One would have thought a more significant difference lay in the column wall thicknesses of the two different impact heights. Apparently flight 175 penetrated/snapped off the thicker steel sections with equal effectiveness.

"The video does show a few slight, perhaps 1° to 2° nose-down pitch attitude at impact". I agree. They were both yawing slightly into the wind, probably, as well as banking. It still would make very little difference to the end result.

As I have repeatedly pointed out, the planes' kinetic energies were equivalent to 1.5 tons of TNT.

But that would be a spherical explosion, whereas the planes' energies could only be applied to their points of contact.
 
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Jazzy

Closed Account
There seems to be a conflation of terms there. There is a designed, static aircraft dihedral that has the wings slightly upswept. This is evident in the drawings of the aircraft.
The dihedral effect, AFAIK, refers to the dynamic changes in the upsweep of the wing under load( When producing lift for instance)
No it doesn't.

It is the name for the restoring force an aircraft with wings with dihedral experiences if it finds itself in a roll position in forward flight.

The sloped wings generate an opposing roll movement (as one wing has become effectively longer than the other) until the wingtips are level with each other.

There is little need for dihedral with high-wing aircraft, as their low CG position will right them.

In the case of most long-haul passenger aircraft, that CG position is at or around the center of lift, so some dihedral is necessary, otherwise the plane would never recover from a roll by itself.

In fighter aircraft such dynamic stability costs energy and prevents extreme maneuvers, so you see cases of anhedral to reduce roll stability: the Harrier has high-mounted wings with the lift generated above its CG. Hence the anhedral you can see.

 
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jaydeehess

Senior Member.
Wrt how the columns are severed( to my mind a better description than "cut") :
Start by thinking of a house in a wind. Not a tall skyscraper, a single storey house. Wind hits the wall and exerts a force on it. If the wind is strong enough it will bend the windows inward until they fail and shatter. If the wind gets even stronger it can push the entire wall in.

Now think of a baseball hitting the window, it may be moving slower than the wind that failed the window but it will concentrate all force on a small part of the window. This causes a local bending of the window and the window fails and breaks before that curvature can affect the wider parts of the window.

Now a bullet, much faster, much smaller. Much smaller local bending and thus quick enough to only produce a small, bullet sized hole in the window as the area if local bending is small but that bending cannot be transmitted to the wider window area before the local area is bent enough to fail..

Back to the 767 into the steel structure. The impact against window openings, no problem right, this will very easily, very quickly fail the glass.
The parts that hit steel( after having hit the insubstantial aluminum cladding) can be thought of as a chunk of aircraft as wide as the steel and as deep as the length of the a/c at that point. It is essentially this mass that is hitting the steel ( yes erosion due to the parts that hit the window rubbing along its sides too which contributes to the inward force on that local length of steel). Now we have a transfer of momentum effect where the momentum of the aircraft parts is being transfered to the column. The column reacts by bending inward the same way a tree bends to a wind. If this occurs fast enough and with enough mass behind it( momentum is mass times velocity) , the column will bend locally before there is time to bend a long length of column( look up moment of inertia, it takes time to change an acceleration) and the column connections will fail (bolts and welds) or even the column itself may yield.
If this takes all of the momentum of the aircraft part then that part will have zero velocity at that point. However, given that it bent the column inwards, even at this that aircraft part is IN the building. More common would be the aircraft part having some velocity left after the columns sever and thus carrying further into the building.
The estimate is that the average velocity of aircraft debris on the inside of the perimeter wall was 100 mph.
That's average though. The parts that came through window openings have slowed much much less. Parts that are heavier such as parts of the wing near the fuselage contain fuel and are thicker between leading and trailing edge and thus contain more mass. As do denser parts such as wheel assemblies_( these after all must be able to support a 100+ ton aircraft and take the forces of landing) and of course various parts of the engines. All of these are moving faster, post entry, than lighter parts.

Clear now?
 
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jaydeehess

Senior Member.
No it doesn't.

It is the name for the restoring force an aircraft with wings with dihedral experiences if it finds itself in a roll position in forward flight. The sloped wings generate an opposing roll movement until the wingtips are level with each other.
Thanks, but has there been a confusion/conflation between the static aircraft's wing upsweep and "dihedral effect".
 

Jason

Senior Member
I don't know if this fireball below warrants an entire thread of its own, and I realize it could be deemed OT, but honestly it has to do with the plane and its wings entry into the WTC.
I've seen this photo pop up from time to time on the CT sites to promote the fact that a missile could've been fired from the plane in order to make it possible for the plane and its wings to enter the bldg because according to them the beams would've stopped the plane's lighter aluminum from entering. Has anyone explained what this "apparent" fireball is prior to the plane hitting the bldg. Is it a reflection off of the glass or what? The picture is of poor quality and I can't figure it out.
 

WeedWhacker

Senior Member
I don't know if this fireball below warrants an entire thread of its own, and I realize it could be deemed OT, but honestly it has to do with the plane and its wings entry into the WTC.
That is the inevitable result of momentum due to the airplane's forward velocity. As the mass of the fuel carried forward, along with all the debris shoved ahead. The suggestion that it "could only be" a "missile" is usually made by those who lack many basic understandings of physics, or (as I've tended to notice over the years) seem to think that what they see in popular action/adventure movies that come out of Hollywood represent reality, and actual physics.

(Referring to CT'ers on CT sites in general, here).
 

Mick West

Administrator
Staff member
How would a missile create a plane-shaped hole?

There's no need to seek explanations for the hole beyond the obvious 500 mph tons of plane.
 
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